The widespread use of the swivel mechanical couplings in devices ranging from spacecraft to automobiles and grocery carts has given rise to a generally widespread need for reliable, practical, low cost methods of transmitting signals through these devices. Coupling of the elements on either side of the swivel by flexible electrical, hydraulic or mechanical cables has not been practical, in many cases, because they will be damaged unless swivel movement is limited to a finite number, e.g. less than 360 degrees. This is often unacceptable. The use of electrical wipers is common in many applications and hydraulic swivels are also a well developed art. What has been lacking up until now is a practical low-cost electro-mechanical device with a configuration well suited for use on casters or steered swiveled wheels.
There is a particular need in the personnel lift industry for devices which convey signals through a rotating joint to be used in a warning or control interlock safety system to transmit information on the ON-OFF status of the brakes or wheel locks which are commonly mounted adjacent to the wheels. This information is sensed at the wheel and must be transmitted in some way to the body of the lift where it can be converted to electrical form for use in control circuitry.
Often a work platform may include a total of four casters, two of which are fixed for rolling in one direction and the other two being swivelable about vertical axes for steering. By judicial movement the presence of two swivelable casters is usually sufficient for required movement of the equipment. Often in work platforms, all four casters will be swivelable.
Similar needs arise in relation to other forms of equipment employing casters or steered or swivelable wheels, in particular where safety of human beings depends on a wheel being locked.
Examples of prior art locking casters are shown in the following patents:
U.S. Pat. No. 3,479,618, L. Maslow, Nov. 25, 1969 PA1 U.S. Pat. No. 3,636,586, Bollinger et al, Jan. 25, 1972 PA1 U.S. Pat. No. 3,751,758, Higbee et al, Aug. 14, 1973 PA1 U.S. Pat. No. 3,828,392, J. Bolger, Aug. 13, 1974 PA1 U.S. Pat. No. 4,037,291, Huempfner et al, July 26, 1977 PA1 U.S. Pat. No. 4,110,866, H. Ishii, Sept. 8, 1978 PA1 U.S. Pat. No. 4,119,156, Wheeler et al, Oct. 10, 1978 PA1 U.S. Pat. No. 4,128,144, H. P. Vassar, Dec. 5, 1978 PA1 U.S. Pat. No. 4,205,413, Collignon et al, June 3, 1980 PA1 U.S. Pat. No. 4,248,445, H. P. Vassar, Feb. 3, 1981 PA1 U.S. Pat. No. 4,269,424, J. L. Gray, May 26, 1981 PA1 U.S. Pat. No. 4,275,962, C. J. Aulik, July 7, 1981 PA1 U.S. Pat. No. 4,336,629, Jarvis et al, June 29, 1982 PA1 U.S. Pat. No. 4,336,630, L. A. Page, June 29, 1982 PA1 U.S. Pat. No. 4,349,937, F. J. Fontana, Sept. 21, 1982 PA1 U.S. Pat. No. 4,349,937, F. J. Fontana, Sept. 21, 1982. PA1 Br. No. 331,619, L. M. Simpson, July 31, 1930 PA1 U.S. Pat. No. 3,845,255, A. Zielke, Oct. 29, 1974 PA1 U.S. Pat. No. 4,140,883, A. Zielke, Feb. 20, 1979 PA1 U.S. Pat. No. 4,167,657, A. Zielke, Sept. 11, 1979 and PA1 U.S. Pat. No. 4,210,787, A. Zielke, July 1, 1980.
In the Maslow patent the brake actuating mechanism operates through the pin of the caster. In the Vassar patent, a bead chain brake actuator extends through the pin of the caster.
In the automotive brake art, indicators have been used to signal brake actuation. Representative of such prior art are U.S. Pat. Nos. 1,673,206 to E. E. Safely issued June 12, 1928 and 2,914,930 to James V. Ralston, issued Nov. 24, 1959.
In the related keyboard art, trapped balls have been used to lock out all but one electrical circuit. Patents disclosing such mechanisms are:
None of these patents recognize the need to signal locked or unlocked condition of a caster assembly and none provide the mechanism which will provide that function.
Even though not all types of elevating work platform lifts are required to have wheel brakes or locks under present law or industrial standards, it is considered that under certain conditions, operator safety may be significantly enhanced when such locks are present. Safety may be further enhanced when in LOCKED or UNLOCKED condition or an INTERMEDIATE position, the lock condition can be signalled to the operator. Better yet, if the elevator mechanism can be blocked during unlocked condition, even greater operator safety often results.
In conditions of operation on a sloping floor, some types of elevating work platforms may present a constant hazard to the operator and to those around him if the platform wheels are not appropriately locked prior to commencement of work or upon elevation of the work station. In some equipment, the brake systems are remotely lockable from the elevated work station but more often than not, they are simple mechanical brakes located at ground level, to be actuated by the operator before he mounts the platform or actuated by a co-worker on the ground.
Up to the present, we are unaware of the use of signal or interlock devices for brakes or swivel locks on the wheels of elevating work platforms. Prior to this invention there has not been a comparable reliable low-cost means of signaling lock condition through the swivel axis of wheels or casters and converting this information into a binary (switched) or analog (proportional) signal.